There has been generally used in a tire a cushion rubber member for correctly shaping an inner surface of the tire to an adequate configuration. Such a cushion rubber member, when it is used for a tire having a belt structure including a circumferential belt and a slant belt, normally employs rubber having relatively low contents of carbon, sulfur and cobalt to reduce rolling resistance of the tire. Cushion rubber therefore generally has relatively low storage modulus and relatively poor adhesion capabilities.
However, in a case of a heavy duty tire which is becoming increasingly flat, in particular, a heavy duty tire having aspect ratio of 70% or less, use of such cushion rubber as described above in a belt structure including a circumferential belt and a slant belt results in a situation in which rubber having relatively poor adhesion capabilities is directly in contact with a slanted belt layer of the slant belt, thereby causing a problem in that sulfur and cobalt contained in belt coating rubber of the slanted belt layer migrate into the cushion rubber to deteriorate adhesion capabilities between steel cords and the coating rubber. Further, in this case, there arises another problem in that the cushion rubber having low storage modulus, disposed close to a side of the circumferential belt, increases strain of the circumferential belt in the cord extending direction.
In view of this, there has been proposed in PTL 1 a method of avoiding the durability problems as described above by providing a cover rubber member having a rubber composition similar to that of the belt coating rubber at an end portion of the slanted belt layer to ensure clearance between the steel cords of slanted belt layer and the cushion rubber.